1. Field of the Invention
This invention generally relates to furniture such as work tables with work surfaces and more specifically to methods and apparatus for adjusting the height of such work surfaces.
2. Description of Related Art
Work tables and like furniture generally provide a fixed height, extremely stable, generally horizontal work surface. In many embodiments such work tables are formed with a horizontal deck assembly or work table supported by upright supports at each of the four corners. More recently, such work tables have been constructed with a pedestal base that supports the table at a rear portion to cantilever the deck assembly forward from the base. This construction eliminates the front upright supports and provides clear knee room at the front, or working area, of the worktable.
Generally corner-supported and cantilevered fixed work tables are supported from below the work surfaces. The plane of the work surface and extensions thereof do not intersect any portion of the work table or its supporting structure. Therefore the work table does not, by itself, limit the size of any item that it supports.
Fixed height work tables are characterized by a fixed working surface height normally set for an average individual in either a sitting or standing posture. Consequently, the work table height is not optimized or ergonomically correct for any specific individual who may be using the work table. In one posture, for example a sitting posture, the work table height will not be optimized for that person in any other posture. If an individual stands, he or she will be forced to stoop. Further, even if the work table height is optimized for one individual in one posture, it probably is not ergonomically correct for other individuals working at the same table even with the same posture. To overcome these problems it has been proposed to provide work tables and other apparatus with adjustable height work surfaces.
The following patents disclose apparatus in which all the structure for adjusting the work surface height lies below the work table or work surface.
______________________________________ 1,927,598 (1933) Schlichter 3,851,854 (1974) Roybal 4,944,366 (1990) Pryor et al ______________________________________
U.S. Pat. No. 1,927,598 (Schlichter) discloses a portable elevating table that comprises a stationary lower plate, a stationary middle plate and a vertically adjustable upper plate. Upright supports in the form of columns at each corner of the table extend between the lower and middle plates and contain means for vertically adjusting the upper plate with respect to the middle plate. A vertical screw within each column attaches to the upper plate and extends to engage a threaded spiral gear located at the top of a corresponding column. A manual operating mechanism rotates a first shaft and connected spiral gear nuts. A gear and chain mechanism interconnects the first shaft with a parallel second shaft with spiral gear nuts. As the operating mechanism rotates, all the spiral gear nuts operate together thereby moving the upper place vertically relative to the middle and lower plates.
U.S. Pat. No. 3,851,854 (Roybal) discloses a scaffold having a stationary frame for supporting vertically movable intermediate and upper frames. The intermediate frame carries vertically positioned, rotatable sleeves at each corner that extend above and below the plane of the intermediate frame. A lower threaded portion of each sleeve screws into a leg that extends vertically from the stationary frame. Each upper sleeve portion has an opposite thread to engage a correspondingly threaded leg that depends from each corner of the upper frame. A common motor drive rotates the sleeves in synchronism to adjust the vertical position of the intermediate frame with respect to the stationary frame and, simultaneously, the vertical position of the upper frame with respect to the intermediate frame.
U.S. Pat. No. 4,944,366 discloses a scaffolding with a rectangular lower frame. Vertically positioned, pneumatically operated cylinders at each corner carry and vertically position an upper work support frame.
Each of the foregoing patents discloses an apparatus for providing an unobstructed adjustable height work surface with all the operating mechanism below the work surface. However, none of these structures is particularly adapted for providing furniture with adjustable height work surfaces. Each requires a support at each corner to provide stability and to provide even movement while the work surface remains horizontal. Thus, this apparatus is not adapted to cantilevered structures. The mechanisms and supports can become bulky and interfere with clearance under the table Moreover these mechanisms are difficult to implement given problems in synchronizing the relative motions at each corner and can become expensive.
The following patents disclose other apparatus that provides work surface adjustment:
______________________________________ 4,294,332 (1981) Ready 4,498,556 (1985) Garton 4,600,085 (1986) Gagnon et al 4,967,733 (1990) Rousseau ______________________________________
U.S. Pat. No. 4,294,332 (Ready) discloses a scaffold comprising a pair of parallel towers. Each tower comprises spaced, vertical rails for supporting vertical gear racks. A self-elevating carriage mounts between the rails. The carriage has a motorized rotatable shaft with two pinion gears for engaging the respective gear racks on the vertical rails thereby to move the carriage vertically on the tower.
U.S. Pat. No. 4,498,556 (Garton) discloses a vertically adjustable platform. The apparatus includes a multi-section, centrally disposed mast with a rack gear. A motor driven pinion engages the rack thereby to adjust the vertical position of the platform with respect to the mast.
U.S. Pat. No. 4,600,085 (Gagnon et al) discloses a platform lift mechanism having four upright telescoping segments. The lowermost first segment is secured to the floor. The uppermost fourth segment is secured to the base of the platform to be lifted. A linear drive comprising an elongated screw and rotatable nut assembly moves the segments relative to each other to position the platform vertically.
U.S. Pat. No. 4,967,733 (Rousseau) discloses a scaffold-like lifting carriage comprising four corner posts, each having a gear rack, and a rectangular platform mounted between the corner posts. The platform has a shaft on each side, each shaft connecting two gear pinions that engage the corner post racks. A motor on the platform rotates the shafts by means of a power chain. As the shafts rotate, the pinion gears advance over the corresponding racks thereby adjusting the vertical position of the platform.
Although each of the foregoing patents discloses apparatus for adjusting the height of a horizontal work surface, each requires portions of the apparatus to extend above the work surface. Moreover, the Schlichter, Roybal, Pryor et al, Gagnon and Rousseau patents disclose structures that support the platform at four different positions. The apparatus in the Ready and Garton patents disclose a cantilever-like work surface, but the support structure extends above the work surface. Moreover, the mechanisms in all of these patents are not constrained by the applications to sizes that can be readily adapted to furniture applications. The Schlichter, Ready, Garton and Rousseau disclose mechanisms in which a motor drive rotates a pinion along a rack to adjust the height. Consequently the rack and pinion must be sized to support the full weight of any load applied to the work surface. For furniture design loads a similar structure will become bulky and unpleasant looking, even with shrouds for covering the mechanisms.